Isidore of Seville

After these plagues, gnats are brought forth. This animal flies through the air suspended on wings. But it is so subtle and minute that it escapes being seen by the eye unless one looks closely. But when it lands on the body it drills in with a sharp sting. If anyone cannot see it flying, he still feels its sting immediately.This sort of animal can be compared with the subtlety of heretics, who drill into souls with the subtle stings of their words. They attack with such cunning that one who is deceived neither sees nor understands the source of his deception. At the third sign the magicians yielded and said, “The finger of God is here.” Those magicians stand for heretics and their animosity.
The apostle states this when he says, “Just as Jannes and Jambres resisted Moses, so too these men resisted the truth. They are corrupt in mind and reprobate in matters of faith. But they will not advance any further. Their madness will be manifested to everyone, just as Jannes’ and Jambres’ was.” The minds of the Egyptian magicians were disquieted by their own corruption, and their power failed at the third sign. They confessed that the Holy Spirit was against them, for the Spirit was in Moses.
The Holy Spirit is put in the third place, and he is the finger of God. Thus the magicians failed at the third sign and said, “The finger of God is here.” The Holy Spirit, well disposed and favorable, gives rest to the meek and humble of heart but, when he is opposed, stirs up disquiet against the merciless and the proud. Those tiny gnats signified this disquiet, at which Pharaoh’s magicians failed and said, “The finger of God is here.”

Daughters of Tyre, daughters of the nations, from species to genus. Through Tyre, neighbor to the land of prophecy, the psalmist signifies all the people who would come to believe in Christ. Rightly, therefore, does he continue: “The wealthy of the earth will all seek your face.” The Lord also threatens Assyria through the prophet Isaiah, saying, “I will destroy the Assyrian in my land, and I will crush him on my mountains"; "and the Lord will destroy Babylon, glorious and famous among the kingdoms, as he destroyed Sodom and Gomorrah.” It is possible that the Lord began to admonish only the city of Babylon at the beginning of Isaiah, but as he spoke against it, he crossed from species to genus and turned to address his word generally toward all the earth. Surely, if he were not speaking against the entire world, he would not have added later: “I will destroy the whole earth, and I will visit evil upon the world,” and other such statements that pertain to the eradication of the corrupted world. Consequently, he also adds, “This is the decision that I have made concerning the whole earth and this is its hand extended over all the peoples.” … He was addressing the entire world under the figure of Babylon, saying, “I will destroy the whole earth, and I will visit evil upon the world,” along with similar declarations pertaining to the world’s extermination. [But] he also turned his attention back toward Babylon, as though from genus to species, and made remarks that relate specifically to that city: “Behold, I am raising Media up against them.” For during Balthasar’s reign, Babylon was taken by Media. So also, the “oracle of Egypt” intends for Egypt to be understood as a personification of the entire world when it says, “And I will cause Egyptians to fight against Egyptians, kingdom against kingdom,” since it is written that Egypt possessed only one kingdom, not many.The fifth rule of time is that the greater part can be implied through the lesser or the lesser through the greater. With regard to the three days of the Lord’s burial, for instance, the whole is taken from the part, since he lay in the tomb neither for three full days nor for three full nights. And the part can be taken from the whole, for after the Lord had established that “the length of a man’s life will be one hundred and twenty years,” only one hundred years passed before the great flood. Also, whereas God predicted that the children of Israel would be slaves in Egypt for four hundred years and would then depart, they were not enslaved for four hundred years, since they had escaped slavery under Joseph’s rule. Yet again, the whole is also here subjoined from the part, since they did not depart Egypt immediately after the four hundred years, as promised, but did so after four hundred and thirty years had transpired. Events that are still in the future but are narrated as though they have already occurred also belong to this rule of time. For example, “They pierced my hands and feet and counted all of my bones,” and “they divided my clothing among themselves,” and similar passages in which what has yet to occur is related as a historical event. Anything predicated of the future, however, is spoken from our perspective. But when the future is said to have happened, it must be understood from the perspective of God’s eternity, since what is still in the future for us has already been accomplished according to God’s predestination, for whom everything in the future has been accomplished.
The sixth rule of time is that of recapitulation, which consists in Scripture returning to what it had already narrated. For instance, when it discussed the sons of the sons of Noah, Scripture said that they had their own language among their own people. Afterwards, however, as though subsequent in time, we read, “And all the earth was of one language, and everyone spoke with one voice.” How, therefore, could the sons of Noah have had their own language if there were only one language for everyone, unless the narrative regressed in order to recapitulate what had already transpired?

They do not understand that God grants to each period of time what is appropriate. As he commanded marriage in the law, so in the gospel does he recommend virginity. In the law, an eye is to be offered for an eye, but in the gospel, the other side of the cheek is to be offered to one’s assailant. The former arrangement was for a weak people, whereas the latter is for the perfect. Nevertheless each order was adapted to its proper time. Yet it is not to be believed on the basis of this change that God is mutable. Instead, it should be proclaimed a miracle that while remaining immutable himself, God gave to each era its own distinctly appropriate order.Sins were of lesser guilt under the Old Testament because only a shadow of the truth, not truth itself, was present therein. For the higher precepts of the New Testament reveal that we are to forsake some of those things to which the people of the shadow of truth were bound. Previously, for instance, fornication and the taking of retribution for injuries were permitted without punishment. In the New Testament, however, they are condemned with severe punishments.
The creed and the Lord’s Prayer replace the whole law in sufficing to obtain the kingdom of heaven for the little ones of the church. For the entire breadth of Scripture is contained briefly in the Lord’s Prayer and the creed. Thus does the prophet Isaiah say, “I heard from the Lord God of hosts about an abbreviation upon all the earth.”